Where is the sudoers file in Solaris? Is it different between Solaris versions (specifically, 9 and 10)?
Solaris has a more advanced privilege system than that. For example you can allow someone access to privileged ports without giving general root access. To do what sudo does, add the "Primary Administrator" profile to the user:
# usermod -P"Primary Administrator" someuser
And then under that user:
$ pfexec command
The profiles are defined in /etc/security/prof_attr. In there you'll see a list of the fine grained privileges in the profile. The user/profile assignments are in /etc/user_attr.